This application claims the priority of German Patent Document 100 30 776.0, filed Jun. 23, 2000, the disclosure of which is expressly incorporated by reference herein.
The invention relates to a method of repairing metallic components, particularly for gas turbines, having mechanically weight-carrying grooves, whose longitudinal edges existing on the component surface are situated at least largely in a plane, and whose actual contour deviates at least locally after the removal and/or displacement of the component material from the desired contour, by the application of an at least predominantly metallic additional material to the actual groove contour as well as by the removing machining to the desired contour, for each groove.
As a rule, weight-carrying grooves in metallic components interact form-lockingly with other components engaging in the grooves. The pairings are usually not free of play and permit relative movements. For this reason, damage may occur after a certain operating period as a result of plastic deformation, frictional corrosion, frictional wear, cracks, chipping-off, etc. which, as a rule, are connected with an at least local widening of the groove cross-section beyond the desired contour. At high component temperatures, as they occur particularly in gas turbines, the mechanical characteristics of metallic materials are considerably impaired so that such damages occur faster and in an intensified form. In order to prevent an exchange of the entire respective component, it is endeavored to repair the groove or grooves in a targeted manner. Different methods are being used or tested for this purpose whose common characteristics consist of that fact that the material is applied in layers to the damaged and therefore no longer dimensionally accurate surfaces of the groove with a certain overdimension and is subsequently partially removed to the dimension during the machining. The used coating methods are metal spraying, galvanic coating or buildup welding. Since, as a rule, the lateral surfaces of the groove are damaged which are situated opposite one another at a narrow distance and virtually xe2x80x9cshadexe2x80x9d one another, it is difficult to impossible to achieve a sufficient uniform coat of material in this case.
In view of the above, it is an object of the invention to provide a method of repairing metallic components with damaged or no longer dimensionally accurate grooves, which permits the restoration of the desired condition in a relatively simple, fast and reliable manner, specifically with respect to the characteristics of the material and the geometry, including the surface quality. A limitation exists in that, in the case of each of the grooves, the longitudinal edges on the surface side of the component should at least largely be situated in a plane. In other words, the direct groove edges formed by the component surface should, if possible, be at one level, in which case the groove bottom will usually also be even and parallel to this level.
The above-mentioned object is achieved by providing a method of repairing metallic components, particularly for gas turbines, having mechanically weight-carrying grooves, whose longitudinal edges existing on the component surface are situated at least largely in a plane, and whose actual contour deviates at least locally after the removal and/or displacement of the component material from the desired contour, by the application of an at least predominantly metallic additional material to the actual groove contour as well as by the removing machining to the desired contour, for each groove, said method comprising the following sequential steps: mechanical abrasive blasting of the groove surfaces by means of a non-oxidic abrasive, closing of open groove ends by a buildup welding of a welding material with the same base as the component material, filling the groove closed on the end side with a soldering powder which has the same base as the material of the component but melts at a lower temperature, without or with a wear-reducing and/or filling additional material, the empty-volume fraction of the soldering powder without or with the additional material being compensated by its accumulation beyond the groove surface, heating the soldering powder in the vacuum to the liquefaction and metallic joining with the component material, the groove being held in a horizontal position opened toward the top, as well as cooling and solidifying in the vacuum, and machining to the desired contour by an extensive removal of the solidified solder. According to the invention, the groove surfaces are first cleaned with a non-oxidic abrasive and activated. Then, if required, the groove is closed at the end by welding, so that virtually a casting mold is obtained which is open toward the top. Next, the groove is filled with a high-temperature solder in powder form which is very similar to the material of the component or partially is identical with it, and is overcharged beyond the groove cross-section. The protruding powder volume should correspond to the empty-volume fraction of the entire powder quantity per groove. After the subsequent heating and liquefying of the solder in the vacuum, the groove is filled to the edge with dense liquid metal, in which case, if required, non-molten metallic or ceramic particles or metal bodies may be contained as an addition. After the metallurgical joining of the solder and the component as well as the cooling and complete solidification in the vacuum, the groove is finished to the desired dimension, a large portion of the solder and of the end-side welding material being removed again. The removed material can be recycled and will therefore not be lost.
Preferred embodiments of the method are described herein and in the claims.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.